It is well known in machining operations to support a workpiece in a vise on a pair of precision parallels. In supporting the work, the parallels take the majority of the vertical force applied to the work during the operation being performed. In addition, the parallels aid visibility, ease the changing of workpieces, avoid damage to the ways, and facilitate lubrication. Of course, because of their precision manufacture, the parallels are intended to provide an exact resting surface for the workpiece.
Because of the environment in which the parallels are used, however, their use does result in several problems which tend to detract from their intended purposes. That is, in machining parts, the operational cycle is typically as follows: place the part onto the parallels and between the jaws of the vise, close the jaws, perform the machining process, clean the surfaces with an air blast, open the jaws, remove the part, clean the area between the parallels with an air blast, reset the parallels against the jaws, place the next part to be processed onto the parallels, and repeat the foregoing steps.
It is during the above-described operational cycle, which includes cleaning, that chips produced may fall or be blown into the area between a jaw and its adjacent parallel and/or on top of the parallel. In addition, the movement of the work may move the parallel away from the adjacent jaw or out one side or the other of the vise, or away from the jaw at an angle, or tilt the parallel at an angle to the ways on which it rests.
The described intrusion of chips and/or the movement of the parallels tend to detract from the intended purposes of the parallels, compromise the quality of the work-support system, and increase the probability that the tolerances specified for the work will not be met. For example, a chip under the work or parallel will cause the work to be at an incorrect angle to the tool being used. Also, if the parallel has moved away from the jaw, the work may tilt in the jaw as the vertical force is applied, again risking ruin of the work. Further, if the parallel is not intimately against the jaw, a tool passing through or past the work may strike the parallel, thereby damaging the tool, the parallel, and/or the work.
Therefore, although parallels are intended to make a machining operation more precise, they are often the source of problems which add to the difficulty of achieving precision. The inconsistent position of the parallels introduces a variable into the process which requires the machinist to devote time and effort in inspecting and adjusting the parallels to insure the integrity of the work-support system.
In an attempt to minimize the above-described problems associated with parallels, machinists commonly resort to two expedients, neither of which is a solution to the problems.
The first expedient is to place double-sided adhesive tape between each jaw and its adjacent parallel and to press the parallel toward the jaw. This technique is difficult to achieve since the surfaces are often covered with a film of oil, and the tape needs to be replaced periodically. Also, there is a gap between the parallel and the jaw equal to the thickness of the tape, and chips tend to accumulate in this gap and on the adhesive tape.
The second expedient is to insert individual compression springs between the parallels to force them against their respective jaws. These springs are difficult to insert, because of the oily surfaces, and they tend to fly out unexpectedly. Moreover, they are unstable and can be dislodged by bumping the parallels, or by a chip driven into the area below the work, or by the cleaning blast of air. In addition, the spring forces available by individual springs, manually compressed and inserted, are too small to retain the parallels against the jaws with any degree of reliability during the operating cycle. In particular, even with such a spring in place, the cleaning blast of air may cause the parallel to flutter against the jaw and thus move or permit the intrusion of chips. An example of this second expedient is shown in U.S. Pat. No. 3,575,406 to Viollet, although this patented device involves specially-made parallels not readily available.
A parallel holding device using a spring band is disclosed in U.S. Pat. No. 4,558,856 to Shaffer, but this device also does not solve the above-described problems with parallels. As with the simple compression springs noted above, the Shaffer device does not apply holding forces at the places or points necessary to achieve control over the parallel. Simple forces directed perpendicularly against the parallel, as with a compression spring and the band spring device of Shaffer, allow the parallel to move laterally of the vise, that is, across the face of the jaw. Moreover, as the jaw gap increases toward the maximum gap width with wider workpieces, or when using the soft jaws instead of the hard jaws to hold the workpiece, the spring forces available with such a device decrease, resulting in smaller holding forces. Conversely, as the jaw gap decreases toward very narrow gaps, the device would tend to interfere with closing of the jaws. Also, the device itself is subject to accidental movement inwardly or transversely relative to the vise or the parallels, for example, by the machinist bumping against the band or otherwise, thus introducing instability to the arrangement.